There is growing evidence for the active role of the joints in pathophysiology. Instead of the joints being the passive victims of important systemic disturbances occurring elsewhere in the body, they may drive the disease to a much greater extent than is presently appreciated. Synovium, which in RA operates as an intraarticular lymph node, could be critical in this regard. One consequence of this paradigm shift would be to put much greater emphasis on treating the joints themselves, rather than extraarticular loci. T-cell-mesenchymal cell interactions in the synovium are particularly important for both T cell activation and induction of inflammation, but the mechanisms underlying mutual co-activation are largely unknown. The proposed study focuses on the relationship between synovial T cell and inflammation in the RA synovium. (1) Co-stimulatory CD28/B7 and CD40/CD40L interactions are required for T cell activation and viability. Intraarticular expression of soluble inhibitors CTLA4Ig and CD40Ig may provide local immunosupression, thereby alleviating the disease without compromising the host immunity. This hypothesis will be tested in animal models of RA using gene transfer of these inhibitors. (2) Our studies established the pivotal role for the transcription factor NF-kappaB in synovial inflammation and hyperplasia, but the mechanisms causing persistent NF- kappaB activation are not known. Direct T cell-mesenchymal cell contacts, particularly CD40/CD40L and CD28/B7 interactions may be critical for NF-kappaB activation and inflammation in the synovium by gene delivery of CD40Ig and CTLA4Ig. (3) One expected finding of our animal studies was that suppression of NF-kappaB in a single joint inhibiting NF-kappaB activation and inflammation in the synovium by gene delivery of CD40Ig and CTLA4Ig. (3) One unexpected finding of our animal studies was that suppression of NF-kappaB in a single joint inhibited inflammation not only in treated, but also in the contralateral, untreated joints. This may have numerous therapeutic ramifications, but the basis for this effect is not known. The induction of NF-kappaB- controlled cytokines and cell adherence molecules in synovial APC, endothelium, and macrophages may be critically important for development and cell adherence molecules in synovial APC, endothelium, and cell adherence molecules in synovial APC, endothelium, and macrophages may be critically important for development of pro-inflammatory Th1 responses in synovial T cells. We hypothesize that local suppression of NF-kappaB activation may shift the Th1/Th2 balance in synovial and circulating T cells toward the anti-inflammatory Th2 subset, thereby alleviating the local and systemic T cell-driven inflammation. This hypothesis will be tested in the proposed project. (4) Closely related, but distinct objective of this proposal is to test a novel concept for designing non-immunogenic adenoviral (Ad) vectors. Ad vectors are uniquely suitable for gene delivery to the synovium, but its immunogenicity precludes clinical applications. As T cell activation is cental to the development of immune responses to Ad transgene, we will examine the feasibility of suppressing the immunogenicity of Ad vectors by expressing CTLA4Ig and CD40Ig genes. Creating immunoprivileged environment in the vicinity of infected cells should permit long-term expression and repetitive administrations.